Electric discharge tube



Feb. 28, 1961 M. KUIPERS ElAL ELECTRIC DISCHARGE TUBE Filed Oct. 20,1958 2 Sheets-Sheet 1 INVENTOR MINNE KUIPERS JAN VAN DER POEL BY wa 1AGENT Feb. 28, 1961 M. KUIPERS ETAL 2,

ELECTRIC DISCHARGE TUBE Filed Oct. 20, 1958 2 Sheets-Sheet 2 INVENTORMINNE KUIPERS JAN VAN DER POEL AGE United States Patent 2,973,449ELECTRIC DISCHARGE TUBE Minne Kuipers and Jan van der Poel, Eindhoven,Netherlands, assignors to North American Philips Company, Inc, New York,N.Y., a corporation of Delaware Filed Oct. 20, 1958, Ser. No. 768,448Claims priority, application Netherlands Oct. 23, 1957 Claims. (Cl.313-271) This invention relates to electric discharge tubes having anindirectly-heated cathode, which tubes are suitable for use in circuitarrangements in which a voltage ditference upwards of 1000 volts mayoccur between the cathode and the filament.

A great difiiculty in such tubes is to provide insulation between thecathode and the filament sufliciently high to avoid breakdown orelectrolysis phenomena also in the hot condition.

It is known per se to arrange an insulated helicallywound wire betweenthe filament and the cylinder of the cathode, by which a large portionof the surface of the filament is left free, while neverthelesssufiicient insulation between the filament and the cathode cylinder isretained and the filament cannot shift with respect to the cathodecylinder. However, breakdown is always liable to occur at the points ofcontact of the insulating layers of the filament wires, supportingwinding and cathode cylinder as a result of electrolysis phenomena andthe like, while a comparatively great spread in the temperature ofdifferent cathodes may occur due to the thermal contact between the saidelements inside the cathodes being not always the same.

A very advantageous embodiment is obtained if, according to theinvention, the filamentary supporting body consists of bare metal whichis secured in the tube quite independently of the cylinder of thecathode. It has been found that, if the filament coated with insulatingmaterial is introduced into a helically-wound tungsten or molybdenumwire, the ends of which are secured independently of the cathode, thefilament is supported and centered sufliciently rigidly to allow apermissible minimum spacing between the helical winding and the cylinderof the cathode. The supporting body may alternatively consist of a wirenetting. If desired, the helical winding or the wire netting may befurther stiffened by means of one or more supporting rods which mayextend in parallel to the longitudinal axis of the cathode. Thesupporting body may advantageously consist of molybdenum.

In many cases it has been found possible to use an ordinary grid ofsuitable size as a supporting body. For example in the case of a cathodeof elongated crosssection, the supporting rods may be arranged in theplane of the long axis of this cross-section.

In order that the invention may be readily carried into effect, it willnow be described in detail, by way of example, with reference to theaccompanying drawing, in which Figs. 1 and 2 show longitudinal sectionsof two embodiments of a tube having a cathode according to the inventionand Fig. 3 shows a cross-section of a cathode as shown in Fig. 2.

Fig. 4 shows another embodiment according to the invention.

In Figs. 1 and 2, reference numeral 1 indicates the bulb of the tube and2 indicates the base, into which contact pins 3 are sealed. In Fig. 1, acathode cylinder 4 is supported in mica members 5. Arranged inside thecathode cylinder 4 is a heater 6, which in this case comprises a foldedinsulated filament 12. The heating element 6 is surrounded by ahelically-wound wire 7, which is supported at its ends independently ofthe cylinder of the cathode, for example by means of supports 8 and 9which are mounted on the mica members 5. One end of the filament is alsoconnected to the support 9. The Whole is surrounded by an anode 13. InFig. 2, the cathode cylinder 10 has a barrel-like cross-section as shownin Fig. 3.

The heater 6, which in the case of the embodiment of Figs. 2 and 3 alsocomprises a folded insulated filament 12, is surrounded by a metal wire7 wound around two supporting rods 11 in the form of an ordinary grid.In this case also, the extremities of the supporting rods 11 areconnected to supports and centered and supported independently of thecathode cylinder 10. As in Fig. 1, these supports are mounted on themica spacers 5.

The bare metal supporting body 7 thus is spaced along its entire lengthfrom the inside surface of the cathode sleeve 10 so as to avoidbreak-down at the contact points.

In Fig. 4 the supporting body consists of a wire netting 14 Althoughonly three diodes are shown as embodiments, the invention is alsoapplicable to tubes containing one or more further grids between thecathode and the anode.

What is claimed is:

1. An electric discharge device comprising an envelope and within theenvelope an indirectly heated cathode assembly capable of withstandinghigh cathode-filament voltages, said cathode assembly comprising acathode cylinder, an insulated heating filament within the cathodecylinder, and a bare metal member within said cathode cylinder butcompletely spaced therefrom and surrounding and engaging and supportingsaid heating filament substantially along its entire length within thecathode cylinder, said bare metal member comprising a wire of asubstance selected from the group consisting of tungsten and molybdenumand helically wound about the filament, and means free of contact withsaid cathode cylinder and supporting opposite end portions of said metalmember within the envelope.

2. A device as set forth in claim 1 wherein a support rod is providedwithin the cathode cylinder and secured to the helically wound metalmember and supporting it within the envelope.

3. An electric discharge device comprising an envelope and within theenvelope an indirectly heated cathode assembly capable of withstandinghigh cathode-filament voltages, said cathode assembly comprising acathode cylinder, an insulated heating filament within the cathodecylinder, and a bare metal member within said cathode cylinder butcompletely spaced therefrom and surrounding and engaging and supportingsaid heating filament substantially along its entire length within thecathode cylinder, insulated spacer means mounted within said envelope,first means supporting said cathode cylinder on the spacer means, secondmeans separate from the first means and free of contact with saidcathode cylinder and supporting one end of said metal member on thespacer means, and third means separate from the cathode cylinder andsupporting the opposite end of said metal member within the envelope.

4. A device as set forth in claim 3 wherein member is a wire netting.

5. A device as set forth in claim 3 wherein the second means includesplural support rods.

References Cited in the file of this patent UNITED STATES PATENTS themetal 2,367,669 Chevigny Jan. 23, 1945 2,444,483 Wing July 6, 19482,870,366 Van Tol J an. 20, 1959

